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Notochord: the rod-shaped supporting axis found in the dorsal part of the embryos of all chordates, including vertebrates

Flexible, non-collapsible rod dorsal to the gut/coelom and below the nervous system, hydrostatic, fluid wrapped in tough connective tissue. As bone does not compact, muscles tensed on one side result in movement instead of shortening the animal. This allows much better locomotion than do cilia for larger animals in water, a crucial victory for later success.

Pharyngeal slits: Slits in the pharynx originally used to gather food, water enters the mouth, passes through pharynx and out gill-like slits, passing through a cavity called an antrium and then outside. In humans, present only in embryo.

Dorsal nerve cord: A neural tube dorsal to the notochord

Postanal tail: Elongation of the body and notochord, nerve cord and muscles past anus into tail, early locomotive function led to success.

The tunicates are located in this subphylum. Along with the subphylum Cephalochordata, these two subphyla make up the invertebrate chordates. Only the tunicate larvae have notochords, nerve cords, and postanal tails. Most adult tunicates are sessile, filter-feeders which retain their pharyngeal slits. Adult tunicates also develop a sac, called a tunic, which gives tunicates their name. Cilia beating within the turnicate cause water to enter the incurrent siphon. The water enters the body, passes through the pharyngeal slits, and leaves the body through the excurrent siphon. Undigested food is removed through the anus. Tunicates are hemaphrodites and can reproduce asexually through budding.In urochordates notochord is confined to larval tail.These lack cranium. These have an open type of circulatory system.Excretion is by neural gland,nephrocytes.there are two siphons through which water enters and exit.they have a tubular heart.they have a tough outer covering.example acidia

The lancelets are located in this subphylum. Along with the subphylum Urochordata, these two subphyla make up the invertebrate chordates. Lancelets receive their name from their bladelike shape. They resemble fish but they are actually scaleless chordates only a few centimeters long. They spend most of their time buried in the sand with their mouths protruding. Fossils of lancelets have been found to be over 550 million years old.

Dropped out sessile stage, what was the larval stage is now sexually reproductive. Includes Branchiostoma (“amphioxus”).

(Vertebra from Latin vertere, to turn). Characterized by separate bones or cartilage blocks firmly joined as a backbone. The backbone supports and protects a dorsal nerve cord. Vertebrates have tissues which are organized into organs which in turn are organized into organ systems.

Vertebral column: Not present in higher vertebrate adults. (In humans, the gel-like, spongy core of the vertebral column is the only remainder. Ruptured or herniated disc is an injury to this.)

Cranium: Composite structure of bone/cartilage. Two functions: 1. Supports sensory organs of head and 2. Encloses or partially encloses the brain.

What evolutionary relationship could we imagine between sessile echinoderms and the higher chordate animals?

Paedomorphic (child-form) hypothesis: basically, evolution of sexual reproduction in what had previously been a larval life stage, or the retention of at least one juvenile characteristic into the adult (adult = sexually reproducing) stage. Some scientists believe that this occurred in a proto-chordate animal lineage. Maybe chordates (and vertebrates) arose from sessile (attached) ancestors. Selection in these proto-chordates maybe began to favor more time in the larval stage, as feeding was more successful or mortality lower in this stage. As larvae got bigger physics shows that the cilia become less efficient for locomotion, favoring the undulating motion allowed by a notochord.

Is this hypothesis crazy? A similar example of this today is Epemeroptera, the mayfly, which has almost abandoned its adult stage. Its one-year lifespan is mostly larval with just a brief day of reproduce-and-die as an adult, which doesn’t even have usable mouthparts.

Tunicate (sea squirt) larva has all four chordate characteristics, although adult sessile (“attached”).

Ostracoderms: extinct Agnathans which had primitive fins and massive plates of bony tissue on their body.

Cyclostomes: "circle mouth" - a group of Agnathans which is still alive in the form of lampreys and hagfish.

Appeared approximately 500 million years ago and dominated the oceans for about 100 million years. The first group of fish to appear. They had neither jaws, paired fins, nor scales, but they were the first organisms with a backbone.

"cartilaginous fish" Appeared about 400 million years ago with bony fish. Includes sharks, skates and rays, and chimaeras. Their skeletons are made of cartilage strengthened by the mineral calcium carbonate.

Synapsids: refers to joined (Greek syn-, together with) parts of skull. Led eventually to mammals. Synapsid pelycosaur >> therapsid >> mammals

Pelycosaur: Sail-backed dinosaur, legs not spread out like lizard but more pillar-like and under body, allowing greater activity and competence in motion, pendulum like rather than constant push-up. Teeth differentiated into different types, for pre-processing of food needed by higher metabolism. Skull changes, bone histology, suggestions of warm-bloodedness.

arose late Jurassic, early Cretaceous. Feathers, skeleton modified for flight. Feathers: epidermal derivative, made of keratin (like fingernails). Carpometacarpis: bears primary flight feathers, parallel to hand parts. Keeled sternum: breastbone, powerful one needed to support flight muscles. Strong, light, occasionally hollow bones. All birds lay eggs (as contrasted to reptiles, which have developed live birthing over 100 independent times.) Why are there no live-bearing birds? Early birds had teeth, lost them. With mammals, only exothermic animals.

Archaeopteryx: “ancient wing”, Jurassic bird-reptile, very dinosaur-like. Good fossils found in Zolenhoffen, German sandstone mine with fine sand, shows feathers clearly, found shortly after Darwin’s publication and used to support his hypothesis. Thick, heavy bones and no sternum, bony tail, not a good flyer but did have primary flight feathers.

Marsupium: (from Greek marsypion, purse or pouch). Gestation period much shorter than in Eutherian mammals, but after leaving the uterus the tiny offspring crawls into a pouch where it completes development latched onto a teat.

Recent molecular (read: genetic) evidence suggests that two different mammal groups may have developed live-bearing ability separately. Instead of being a “rough draft” for placental-style live bearing, perhaps the marsupial pouch approach is another solution to the same problem. Advantage: in tough times the parent can pitch out the offspring and increase its own chance of survival.